This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-137380 filed May 10, 2000.
The present invention relates to a vehicle navigation having guide representation of branch roads, and particularly to a vehicle navigation which provides an appropriate guide representation concerning a junction having branch roads.
Various vehicle navigation systems are known as equipment for enabling a driver to arrive at the destination without difficulty. The navigation systems detect the present position of a vehicle by GPS (global positioning system) or the like as the vehicle travels, so that they represent the present position with a road map on a display. The navigation systems also provide a route guidance to the destination visually on the displayed road map and with voice message from a speaker.
Some navigation systems provide a branching guidance to guide an exit while traveling an expressway. For instance, the guidance is made by providing a voice message xe2x80x9cExit for XXX direction is about 700 meters aheadxe2x80x9d when the vehicle approaches a position which is about 700 meters away from the branch road (exit). This conventional guidance provides only limited information such as names of directions which specify branch roads. Thus, it is difficult to match the guidance with guide signboard provided in correspondence with the branch road.
For instance, a driver may mishear or miss voice messages of the names of the directions when the guidance is provided with a voice message. The driver may also misread or miss the names of the directions written on the guidance signboard even if the driver catches the voice messages. Thus, the branch roads which the driver should take cannot be taken properly, if the driver fails to match the voice message guidance with the written information on the signboards.
Other navigation systems provide the branching guidance by the number of exits which the driver should pass on an expressway. For instance, the guidance provides a message xe2x80x9cTake N-th exit.xe2x80x9d However, this system requires a driver to count the number of the exits. If the driver miscounts, the driver cannot take the right exit to the branch road which should be taken.
The present invention has therefore an object to provide an appropriate route guidance including a branching guidance.
According to the present invention, a navigation system provides a travel route guidance to a destination and a branching guidance for indicating a branch road to be taken from a presently traveling road in the course of the travel route guidance. A control unit checks whether a branch road number which is specific to the branch road to be taken is available in a road map data stored in a memory. The branch road number may be an exit number of an expressway or a rotary road, and identical with a number actually indicated on a roadside signboard which indicates the branch road. The control unit retrieves the branch road number from the memory if available in the memory, and indicates the retrieved exit number in a vehicle. The retrieved branch road number is preferably provided as a voice message.